It has long been recognized that the heating of food within an oven enclosure will be more uniform throughout the food product if it is rotated during the heating process. This is particularly desirable where the product is baked such as cakes, breads or the like.
Early recognition of this concept is found in U.S. Pat. No. 416,839 to Howard and U.S. Pat. No. 557,344 to Shaw.
With the advent of microwave cooking the principle involved became even more important due to the rapidity of baking or cooking the finished product. In microwave cooking the inner and outer portions of the product within the oven are both heated simultaneously and quickly to a normal cooking temperature. However, the microwave energies are not uniformly distributed within the oven enclosure resulting in unevenness in cooking throughout the body of the food product. It is accordingly even more desirable that the food product be slowly rotated during baking within a microwave oven. As the product is rotated the food passes through uneven microwave patterns to create an even cooking effect eliminating any so-called "hot spots" in the product mass. The "hot spots" are not in fixed locations but may shift over time and with varying "load" as different shapes and sizes of foods are cooked.
Accordingly others have invented structures specifically designed for microwave ovens. Examples are U.S. Pat. Nos. 2,632,838 to Schroeder and 3,177,335 to Fitzmayer et al, both of which show the use of turntables built into the microwave oven itself thus allowing the driving motor to be disposed outside of the oven interior and hence outside of the oven environment containing ultra-high frequency electromagnetic wave energy (hereinafter referred to as "microwave").
More recently, portable turntables for use in microwave ovens have been developed. An example is U.S. Pat. No. 4,258,630 to Jorgensen et al, which shows a portable turntable with all of the metal parts shielded within a relatively smooth metal enclosure where they are in an area of no microwave energy, such energy being excluded by the shielding so as to prevent arcing problems.
Additionally, a portable turntable powered by the microwave energy within a microwave oven is disclosed by U.S. Pat. No. 4,254,319 to Beh et al. This patent discloses a device wherein water is heated by the microwave energy to generate steam which powers a small turbine geared to drive the turntable. The exclusion of all metal from the structure makes it suited for the microwave oven environment. However, this structure is not suited to a practical turntable for a number of reasons. Heating the water consumes a good deal of power so that less power is available to cook the food resulting in increased cooking time. There is no steam power until the water is boiling so the turntable does not operate until then. When steam is produced it is produced rapidly for a fairly short period and is released into the oven where it may create problems. After the water has been consumed for production of steam, the water must be replaced for further operation.
A second microwave powered turntable is disclosed in U.S. Pat. No. 4,219,715 to Mandle et al, which discloses a structure driven by an electric motor and drive gearing. The motor is energized by electricity derived from the microwave energy in the oven. Loop antennae are disclosed sized to pick up microwave energy to be conducted to a suitable rectifier. However, deficiencies in the loop antennae and lack of a sufficiently powerful rectifier circuit result in insufficient power to drive an electric motor.
It is accordingly desirable that a turntable construction be provided in the way of a portable accessory powered by the microwave power within a microwave oven and utilizing improved antenna and rectifier structures.